USE OF DEOFIX TM IN DEODORANT PRODUCTS 259 Panzarella (18) and Shelley (19) in the late 1940s and early 1950s. These authors showed that axillary microbial growth was the primary source of malodor. With this under- standing, the search for new deodorant ingredients largely focused on antimicrobial agents, the concept being that reduction in axillary microbial growth would result in less odor. Since then, almost all commercial deodorant ingredients have been based on biocides (Triclosan currently being the most popular). However, antimicrobial agents, such as Triclosan, are not without their detractors. Essentially two types of concerns have been voiced. Antimicrobial agents can change the commensal flora on the skin. This modification in the natural skin flora balance may predispose the skin to opportunistic infections (20). With time, it might also give rise to relatively resistant strains of bacteria. A second concern relates to the widespread release of antimicrobial agents and their biodegradation residues into the environment. These concerns have resulted in some of these agents being precluded from use in some European countries as well as elsewhere. Other, non-antimicrobial approaches to achieving deodorancy have been advanced as our understanding increases as to the nature of the odiferous materials and the metabolic pathways by which they are produced. Makin and Lowry (3) recently published a complete review of these approaches. Unfortunately, to date, none of these approaches have been proven to be more effective than antimicrobials. This paper reports on the use of Deofix TM, a metal ion chelator with unusually high affinity and specificity for first transition series elements, as a new deodorant ingredient. Chelators, in themselves, are not new as deodorant ingredients. Ethylenediaminetetra- acetic acid (EDTA), aside from being widely used as a booster for the activity of preservatives, has been sometimes included in deodorant formulations. EDTA deriva- tives have been claimed to have synergistic activity with agents such as Triclosan and quaternary ammonium germicidal compounds (21). The presumption is that their ac- tivity is related to their ability to chelate metal ions required for bacterial growth. First transition series elements such as iron, zinc, manganese, and copper are essential for microbial proliferation. For example, oxidative metabolism relies upon iron-containing heme enzymes, DNA synthesis requires iron-containing ribonucleotide reductase and nucleic acid polymerases require zinc as a coenzyme. The iron ions in iron-containing enzymes are in a form so tightly bound that they essentially cannot be removed by chelating agents. What chelating agents can do is lower the environmental concentra- tion of these metal cations to a level where there is an insufficient amount to form new metal-containing enzymes required for cell duplication. Since only trace quantities of these metals are required, chelating agents with unusually high affinity (i.e., very low thermodynamic equilibrium constant) and specificity are required. In comparison to Deofix TM, chelating agents like EDTA do not form highly stable chelates with first transition series elements. The iron chelate with Deofix TM is more than 10 9 times more stable than the iron chelate with EDTA (5). This means that when both chelators are present in solution in the same concentrations, the available free iron (FelII) in solution is 109 times lower with Deofix TM than with EDTA. We believe this explains, at least in part, the biological and deodorant activity observed with Deofix TM. This mechanism of action fits nicely with the low cytotoxity observed with Deofix TM and the results with human foreskin fibroblasts. Deofix TM lowers the availability of first transition series metals to inhibit cell replication but does not remove these metals from

260 JOURNAL OF COSMETIC SCIENCE already existing enzymes that would cause permanent cell damage. Thus, using Deofix TM in the incubating media with human foreskin fibroblasts prevented cell rep- lication. However, the replication of cells resumed normally when the Deofix•M media was replaced with media free of Deofix•. Experiments with Deofix TM and microorganisms demonstrated relatively low minimum inhibitory concentrations but considerably higher minimum lethal concentrations. This further supports the mode of action: limiting the availability of essential first transition series elements while not disrupting the function of existing enzyme systems containing these elements. The extended duration of the deodorant effects observed with Deofix TM (high efficacy even 48 hours after last treatment) may also be explained by its proposed mode of action. A conventional antimicrobial deodorant would be expected to function only as long as the skin surface concentration of the antimicrobial agent in the axilla remains at a level required to inhibit microbial growth. With time, however, deodorant ingredients ap- plied to the axilla are inactivated by skin and sweat components, rubbed off, diluted by sweat, or otherwise transferred to articles of clothing, thereby reducing their antimi- crobial effects in the axilla. The principle is simple: if you remove or otherwise inactivate the antimicrobial agent, you also lose deodorant efficacy. With deodorants that function like DeofixV• (by complexing elements essential for microbial proliferation), the situation is very different. On application to the axilla, DeofixVM forms very strong complexes with any first transition series metal ions that are present. Removal of these complexes from the axilla surface by any of the mechanisms proposed above does not decrease the deodorant efficacy. Resumed rapid bacterial mul- tiplication (and odor generation) can only occur when the trace elements that were removed by the DeofixV• are replaced. The replacement may come from skin cells, sweat, or external sources. The extended deodorant efficacy observed with Deofix TM suggests that this replacement occurs slowly. Finally, it should be mentioned that DeofixV• may be exhibiting some of its deodorant efficacy based on its antioxidant properties. The oxidation of sebum components has been proposed as one route in the production of underarm malodor. The use of anti- oxidants with antimicrobial agents has been reported for deodorant use (22-24). Simi- larly, it has been proposed that lipoxidases are capable of catalyzing the hyperoxidation of polyunsaturated fatty acids in sebum, which can further decompose into odiferous aldehydes, ketones, and acids. Inhibition by antioxidants of the hyperoxidation might also lead to reduction of malodor. Oxidation in biological systems usually involves the formation of reactive oxygen species (ROS). ROS have been invoked as a major cause of skin damage and aging. One of the most damaging ROS species is the hydroxyl radical. Formation of hydroxyl radicals is catalyzed by trace quantities of iron or copper via Haber-Weiss pathways. In these reactions the reduced form of ionic iron, Fe(II), or ionic copper, Cu(I), initiates the hydroxyl radical-generating reaction. Because of the central role of iron in catalyzing the formation of free radicals, as well as other toxic oxygen species, the use of iron chelators to reduce the tissue concentration of catalytically active iron has been examined. However, unless the chelator can reduce the iron concentration to below the catalytic levels required for free radical generation, and the chelated iron is not catalytically active in Haber-Weiss pathways, they cannot